The polycyclic aromatic hydrocarbon (PAH) 3-methylcholanthrene (MC) is a known initiator of ovarian granulosa cell tumor in mice. A prerequisite to initiation of ovarian tumors appears to be depletion of primordial follicles from the ovaries of PAH sensitive mice. When C57B1/6N (B6) mice are treated with MC nearly all of the primordial oocytes are destroyed within 3 days. Ultrastructural studies revealed that the morphological appearance of damaged oocytes in ovaries of treated animals is similar to spontaneous atretic oocytes. Because of these similarities, it might be possible to utilize induced atresia in studying the normal atretic process.